In the current communication system, extensive research is being conducted into a high quality multimedia service capable of transmitting mass data at a high speed. Different from wired channel environments, wireless channel environments existing in such a communication system include several factors, such as multipath interference, shadowing, propagation attenuation, time-varying noise, interference, and so forth, all of which cause communication errors in the communication system. Accordingly, a receiver receives data which is seriously distorted from data actually transmitted from a transmitter because the factors have been reflected in the data, and such a distortion degrades the performance of the entire communication system.
One of the technologies proposed to solve the performance degradation problem in the communication system is a multiple input multiple output (MIMO) technology. The MIMO communication system can obtain a full diversity gain and a full rate gain by using a transmit antenna diversity scheme. According to the transmit antenna diversity scheme, transmission gain is determined depending on channel states, and on whether the transmission path of a transmission antenna corresponds to an open loop or a closed loop.
According to the open-loop MIMO communication system, a transmitter estimates the data reception quality of a receiver, calculates transmission power, and transmits data with the calculated transmission power. According to the closed-loop MIMO communication system, generally, a transmitter receives a feedback of data reception quality from a receiver through a feedback channel, calculates transmission power by taking the fed-back data reception quality into consideration, and transmits data with the calculated transmission power.
Meanwhile, when receiving data from a transmitter in the closed-loop MIMO communication system, a receiver feeds back information about reception quality of the received data to the transmitter through a feedback channel. Especially, in a closed-loop MIMO communication system based on an orthogonal frequency division multiplexing (OFDM) scheme, since information about reception quality is fed back for every subcarrier, the amount of reception quality information to be fed back is large, and such a large amount of reception quality information significantly increases the overhead of an uplink.
However, when the amount of resources for the feedback channel is restricted in the closed-loop MIMO communication system, the receiver cannot transmit proper feedback of reception quality information according to each subcarrier. As a result, the transmitter cannot receive proper feedback of reception quality information according to each subcarrier, so that the transmitter inaccurately calculates transmission power, and transmits data to the receiver according to the inaccurately calculated transmission power. As described above, when the amount of reception quality information is greater than the amount of resources for the feedback channel, the performance of the closed-loop MIMO communication system is degraded.